Four-wheel-drive vehicles

Claim 1

A four-wheel-drive vehicle comprising drivable front and rear sets of wheels, the wheels of at least one set being connected by a differential gear; a prime mover; change speed means having an input and an output, the input being arranged to be driven by the prime mover and the output being connected by a first driving connection to drive the wheels of said one set; a two-part second driving connection between the wheels of said other set and either the first driving connection or said output, the parts of said second driving connection being drivingly connected respectively to the wheels of said other set and said output or first connection; a gear pumping device comprising first and second meshing gear means connected respectively to said parts of the second driving connection, relative rotation of said gear means resulting from a difference in the speed of rotation of said front and rear sets of wheels causing pumping of non-gaseous fluid; a circuit for the pump fluid; and variable orifice means in the circuit and operable by the pressure of the fluid being pumped to increase the resistance encountered by fluid being pumped around the circuit with increase in the speed of relative rotation between the first and second gear means whereby, as said difference in the speed of rotation of said front and rear wheels increases, an increasing proportion of the torque previously applied to said one set of wheels by said prime mover is applied to said other set of wheels.